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Colorimetric fluoride detection in dimethyl sulfoxide using a heteroleptic ruthenium(ii) complex with amino and amide groups: X-ray crystallographic and spectroscopic analyses†
Tomoki Hasegawa,Noriharu Nagao
RSC Advances Pub Date : 09/07/2022 00:00:00 , DOI:10.1039/D2RA03593F
Abstract

A bis-heteroleptic ruthenium(II) complex, [Ru(Hdpa)2(H2pia)]X2 (1·X2; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; H2pia = 2-pycolinamide; OTf = CF3SO3), was synthesized and spectroscopically and crystallographically characterized. The crystal structures of 1·Cl2·2.5H2O and 1·F2·2EtOH revealed essentially identical geometries for the 12+ dication; however, the dihedral angle between the two pyridyl groups in the Hdpa ligands, which represented the degree of bending of the bent conformation, was affected by hydrogen-bonding interactions between the NH group and counterions. In 1·F2·2EtOH, one of the Hdpa ligands had an unusually smaller dihedral angle (15.8°) than the others (29.9°–35.0°). The two NH groups of each Hdpa ligand and the NH2 group of the H2pia ligand in 12+ acted as receptors for F anion recognition via hydrogen-bonding interactions in a dimethyl sulfoxide (DMSO) solution, and the reaction showed an unambiguous color change in the visible region. Upon the addition of tetra-n-butylammonium fluoride to the red DMSO solution of 1·(OTf)2·H2O, the solution turned dark brown. 1H NMR analysis and absorption spectroscopy of the reaction between 12+ and the added F anions revealed that the F anions did not distinguish between the two amino groups of Hdpa and the amide group of H2pia, although they were in different environments in the DMSO solution. A tris-F-adduct with 12+, 1·F3, was formed when sufficient F anions were present in the solution, despite the presence of four NH protons in 12+. Time-dependent DFT calculations of 12+ and 1·F3 were consistent with their absorption spectra.

Graphical abstract: Colorimetric fluoride detection in dimethyl sulfoxide using a heteroleptic ruthenium(ii) complex with amino and amide groups: X-ray crystallographic and spectroscopic analyses
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